TSSA - The Simplest Symmetrical Amplifier
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 11th September 2012, 07:02 PM #1051 padamiecki   diyAudio Member   Join Date: Mar 2004 Location: Krakow Jay your flag is upside down __________________ regards, Pawel
smartx21
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Quote:
 Originally Posted by Joachim Gerhard Christophe, would more open loop gain result not only in a higher damping factor but also less distortion ?
Well, when we increase the gain factor of 1 stage in an amplifier (with no other change) we often increase its own distortion. (= We reduce its local feedback) In a global loop, increasing feedback to compensate this adding gain will reduce back the global distortion. Did the result better or worse than before ? Hard to predict !
I think we can have a more accurate answer looking at the slewrate.

sonnya
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Join Date: Oct 2001
Location: Denmark
Quote:
 Originally Posted by Joachim Gerhard I am not sure, is that 3V input or output ? If it is 3V input then his simulation shows much lesser harmonic distortion as other versions of the TSSA i have seen. Christophe, would more open loop gain result not only in a higher damping factor but also less distortion ?
Basicly the system closed loop gain is calculated with the following formula..

closed loop gain = A/(1+(A * Beta).

A is openloop gain.

Beta is the feedback network. For inverted configuration it is:

Beta = 1/(RF/RG)

For noninverted configuration it is:

Beta = 1/(1+(RF/RG)).

The TSSA as example. You will have a openloop gain A = 158.

Beta is 1/(1+(1K/100)) = 1/11 = .09091

Closedloop gain is: 158/(1+158*.09091) = 10.28.

In comparison with this one TSSA - The Simplest Symmetrical Amplifier who has a A = 1.000.000..

It is really bad with the TSSA. But it is helped along with CFP input pair wich have local feedback that lowers distortion from the input pair.

Also the mosfet runs in class A .. So the most of the time we do not need to struggle with crossover distortion.

The SSA maybe be better in terms gain. but it also have some unlinear parameters the TSSA does not have...

There is several parameters we can work with.

Reduce RF and RG to 499R and 49.9R => A = ~300

use double lateral mosfet => A = ~600.

Raise the resistor R8 and R7 to 2K => A= ~1200.

Whe have now reduced the distortion 8 times. And Zout is also lowered 8 times.

The system gain means that we 2VRMS to get maximum power. Most DACS and CD players can manage that.

 11th September 2012, 08:33 PM #1055 Joachim Gerhard   diyAudio Member     Join Date: Mar 2009 R8 and R8 in what schematic ?
 11th September 2012, 08:36 PM #1056 sonnya   diyAudio Member     Join Date: Oct 2001 Location: Denmark http://sitosite.dk/amps/TSSA-01300712.pdf RF is R11 and R12 and RG is R13 and R14.
 11th September 2012, 08:44 PM #1057 Joachim Gerhard   diyAudio Member     Join Date: Mar 2009 So lowering the feedback resistors raises the open loop gain. Is that the same mechanism as in CFB opamps ? Lowering too much would then cause instability.
 11th September 2012, 08:47 PM #1058 Salas   diyAudio Chief Moderator     Join Date: Oct 2002 Location: Athens-Greece May I use 1K/50R RF/RG for 26dB and still be kinda decent?
 11th September 2012, 08:54 PM #1059 sonnya   diyAudio Member     Join Date: Oct 2001 Location: Denmark Joachim: Exactly.... Except there no such thing as a stable amp with out Cdom capacitors in one form or another. In my amp it is C12 and C13. Thats why i asked if the SSA design are stable into 10uF load (I think Quad electrostates are close). My designs are not stable without extentions in the design... I really dont think the SSA are completly stable... Go for Megahertz they all say. Some of it is true... But you need take into account what you pick up of noise and how close you will come to instabillity.. They are now 47pF but i would suggest 220 - 330pF with all the changes above....
sonnya
diyAudio Member

Join Date: Oct 2001
Location: Denmark
Quote:
 Originally Posted by Salas May I use 1K/50R RF/RG for 26dB and still be kinda decent?
Yes of course, and you will preserve the Zout.

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